Device and method for ion shunt current elimination - Patents.com

Abstract

The present invention provides a bipolar system that includes two or more electrochemical cells and a bipolar connector operable as a shunt current suppression device disposed in the flow path of an electrolyte solution flowing between the cells.

Description

[Technical field]

[0001] The present invention generally contemplates devices and methods for ionic shunt current elimination in electrochemical systems. [Background technology]

[0002] The bipolar electrochemical cell connection method is commonly used in the electrochemical industry (batteries, supercapacitors, fuel cells, electrolyzers) for multi-cell stacking and connection. It was developed to reduce power losses due to series resistance. The method requires that the anode of one electrode set be connected to the cathode of the adjacent electrode set while avoiding or minimizing electrolyte connections between the electrode sets. In electrochemical thermally activated chemical cell (E-TAC) electrolyzers [1, 2], the anodes and cathodes of a single stack (or roll) are contained within a single compartment and electrolyte flows between adjacent stacks. Therefore, bipolar connectors (BPCs) must provide electrical and ionic insulation between adjacent stacks, while at the same time providing passage for electrolyte and product gases through the reactor.

[0003] Two configurations of electrochemical cell stacks are known.

[0004] Monopolar cell stacking (as shown in Figure 1) - cells are connected in parallel such that the positive electrodes are connected together and the negative electrodes are connected individually. This connection can be between individual cells by wiring to the cell housing, or between electrodes connected and immersed in the same cell solution sharing the same electrolyte environment. In such a monopolar configuration, the system current is the sum of the currents and the system voltage is the same as the voltage of each of the individual cells. Thus, due to resistive effects, the electrodes may heat up with increasing current. From a mechanical point of view, this is the simplest cell configuration in electrolyzer assembly, where all cells in the stack are immersed in the same electrolytic environment without shorting.

[0005] Bipolar cell stacking (shown in Figure 2) - In such a configuration, the cells are connected in series and each positive electrode is connected to the negative electrode of the adjacent cell. This connection can consist of individual cells by wiring to the cell housing or to electrodes connected and immersed in the same cell housing, but in contrast to the monopolar configuration, electrical isolation of the electrolyte (ionic disconnection) is required between the individual cells to avoid short circuits. The positive and negative electrodes of adjacent cells are usually connected by a bipolar plate, a common current collector between the electrodes, providing a physical barrier between the cells and the necessary electronic conductivity. The system voltage is the sum of the cell voltages. The system current is the current of each of the individual cells. Thus, resistive heating associated with the applied current is minimal. However, the challenge of such a system is to overcome possible "soft shorts" and leakage currents, especially in flow-based systems where the electrolyte flows and has a common reservoir for all cells. publications [1] International Patent Application No. PCT / IL2015 / 051120 [2] International Patent Application No. PCT / IL2019 / 050314 [3]US2019 / 218678 [4] US4,277,317 [5] US3,666,561 [6] US3,634,139 [7] US3,522,098 [8] US3,537,904 [9]US2018 / 342751

[10] US2019 / 252709

[11] US2014 / 060666

[12] CN106207240

[13] WO2016 / 128038

[14] US2014 / 272512

[15] US2012 / 308856

[16] US4,377,445

[17] WO2007 / 131250

[18] JP62108465

[19] JP59127378

[20] US2014 / 287335 Summary of the Invention

[0006] Flow-based systems, e.g. electrolyzers, fuel cells, and flow batteries, use bipolar plates placed between the cathode and anode of adjacent cells. The bipolar plates act as a common current collector while creating a physical barrier between the cells. The barrier has ionic conductivity to avoid "soft" short circuits, which would cause current leakage if adjacent electrodes were in direct and intimate contact with the same electrolytic environment. The mechanism of this current leakage in a bipolar stack is shown in Figure 3.

[0007] The potential gradient between the electrode pair (EP1 and EP2 in Figure 3) causes a leakage current (l leak ) flows between the anode of one electrode set EP1 and the cathode of the other electrode set EP2. This is a faradaic current with a high overpotential. Its value is the reaction current l that flows between the electrodes in the same electrode set. react1 , l react2 The leakage current l leak This results in significant power losses during the electrolysis process. To reduce current leakage, it is necessary to provide ionic electrical isolation between adjacent electrode pairs while still allowing the electrolyte to connect, which conventional bipolar plates are unable to do due to the physical separation between the two cells.

[0008] In a typical electrochemical thermally activated chemical cell (E-TAC) electrolyzer, the anodes and cathodes of a single stack (or roll) are housed in a single compartment, and electrolyte flows between adjacent stacks. Thus, bipolar connectors (BPCs) located in such electrolyzers must provide electrical and ionic insulation between adjacent stacks (electrolysis / electrochemical cells / cell-stacks) and also allow electrolyte and product gases to pass through the reactor. The E-TAC system is configured to continue functioning as long as reactants are supplied to the cells and reaction products are removed. This maintains a substantially stable and unaltered system. Due to the electrical conductivity of the liquid electrolyte and the electric field potential gradient, ionic shunt currents can flow between individual cells and between cell stacks by traveling the paths of the conductive liquid electrolyte. The presence of ionic shunt currents can reduce the charge storage and discharge capacity of each stack and also reduce the energy efficiency of the overall system.

[0009] In the prior art system shown in Figure 4, the bipolar plates (Device #1) form a conductive physical barrier between the electrochemical cells to prevent electrolyte flow and prevent ionic conductivity between the cells while allowing electrical conductivity between the anodes and cathodes of adjacent electrochemical cells. The shunt current barrier (Device #2) counteracts the shunt current between the electrochemical cells by forming a non-conductive flow path that allows electrolyte flow between adjacent electrochemical cells and prevents ionic and electrical conductivity.

[0010] Unlike the systems and methodologies of the art, as shown in FIG. 5, the inventors of the technology disclosed herein have developed a system configured to allow uninterrupted electrolyte flow through a bipolar connector (BPC) that is not a bipolar plate, placed between any two electrochemical cells or between any two electrochemical cell stacks while maintaining cell activity in terms of completely avoiding or minimizing leakage current. The system also ensures electronic conductivity by allowing electrical conductivity between the anode and cathode of adjacent electrochemical cells. This unconventional approach negates the use of conventional bipolar plates to form a physical barrier between cells to prevent electrolyte flow. In the system of the present invention, no such physical barrier exists and the flow path of the electrolyte solution remains open.

[0011] Thus, in a first aspect, the present invention provides a bipolar system comprising two or more electrochemical cells each connected to another electrochemical cell via a series electrical connection (in a series connection), and a bipolar connector, BPC (operable as a shunt current suppression device) disposed in a flow path of an electrolyte solution flowing between the cells, said BPC (disposed between each two of the two or more electrochemical cells) configured to allow an uninterrupted flow of electrolyte solution and to prevent or reduce or mitigate or minimize ionic shunt currents from crossing said device, wherein said system is devoid of bipolar plates or bipolar separators.

[0012] The present invention further provides a system comprising a stacked arrangement of two or more electrochemical cells, each cell in the arrangement configured and operable to allow directional flow (along a flow path) of electrolyte solution between the cells in the stack and connected in series to another cell in the arrangement via a BPC (operable as a shunt current suppression device) that prevents ionic current leakage, the system being a bipolar arrangement without a bipolar plate or bipolar separator.

[0013] Further provided is a system comprising one or more bipolar stacks, each stack comprising two or more electrochemical cells each comprising an electrode assembly and an electrolyte solution, the cells in each stack being arranged in series and fluidly associated via inter-cell conduits defining a flow path for the electrolyte solution between the (adjacent) cells, the conduits comprising (or being provided with) a BPC configured and operable to reduce or prevent current leakage (operable as a shunt current suppression device) while maintaining the flow of the electrolyte solution, the system being provided in a bipolar arrangement, wherein each of the stacks is free of bipolar plates or bipolar separators.

[0014] Also, a plurality of electrochemical cells, e.g., E-TAC cells, arranged in a plurality of stacks, each cell connected in series to another cell in the stack; a means for supplying an electrolyte solution to the stack / cell as a shared electrolyte; Also provided is an electrochemical system comprising an electrolyte conduit configured as an electrolyte flow path, the electrolyte conduit being provided with a BPC configured and operable to reduce or prevent current leakage while maintaining an (uninterrupted) flow of electrolyte solution, the system being provided in a bipolar arrangement, wherein each of the stacks is free of bipolar plates or bipolar separators.

[0015] The present invention further provides an electrochemical system configured and operable to minimize shunt current in a system, e.g., an E-TAC system, the system comprising a plurality of stacks, each stack comprising a plurality of electrochemical cells connected in series, the system comprising an electrolyte solution shared by the plurality of cells, the solution flow path being provided with a BPC (shunt current suppression device) allowing electrolyte to flow through the path and the BPC to reduce (minimize or eliminate) ionic shunt current compared to a system without the BPC.

[0016] As disclosed herein, electrolyte flows from an electrolyte storage tank through pipes to the stack (with or without pumps and heating / cooling devices as required by the process), through each of the cells in the stack and through bipolar connectors to the stack outlet, after which the electrolyte solution is returned to the electrolyte tank or to the gas / liquid separator, depending on the configuration of the system.

[0017] In the system of the present invention, the electrolyte or aqueous solution circulates through the cells and stacks, and optionally through one or more shunt current suppression devices, or BPCs, present in the electrolyte pathway and that may be provided between any two cells and optionally between any two stacks, as shown in FIG. 5. Typically, the electrolyte solution is shared between the cells and between the stacks in a given stack. Thus, the system of the present invention may be provided with one or more manifolds that allow the circulation of the electrolyte solution to and within the system. This circulation is further enabled by the presence of channels or conduits or other components in which the BPCs or shunt current suppression devices are provided.

[0018] The system of the present invention without bipolar plates or separators is a bipolar connected stack arrangement. In such an arrangement, several single electrochemical cells can be assembled in series to form a "stack" of electrochemical cells. Several stacks can then be further assembled. As described for individual electrochemical cells, the stack is also arranged with positive and negative current collectors that allow electrons to flow through the cell stack along an axis perpendicular to the ion transport membrane and current collectors during electrochemical charging and discharging.

[0019] In some embodiments, the system or each of the stacks in the system or each electrochemical cell in a stack of the system is an electrochemical thermally activated chemical cell (E-TAC) electrolyser [1, 2]. As described herein, in an E-TAC, the anode and cathode of a single stack are housed in a single compartment and electrolyte flows between adjacent stacks. Thus, bipolar connectors (BPCs) provide, on the one hand, electrical and ionic insulation between adjacent stacks and, on the other hand, the passage of electrolyte and product gas through the reactor.

[0020] According to another aspect, the present invention provides a system for producing hydrogen gas and / or oxygen gas, the system comprising at least one stack of two or more electrochemical thermally activated chemical cells ("E-TAC cells"), each of the two or more cells configured to hold an electrolyte solution and comprising an electrode assembly having a cathode electrode and an anode electrode, the two or more cells configured to produce hydrogen gas in the presence of an electrical bias and to produce oxygen gas in the absence of the bias; Each of the two or more cells in the at least one stack is configured and operable to allow directional flow of electrolyte solution between the cells and is connected in series to another of the two or more cells in the stack via a BPC, i.e., an ionic current interrupter or shunt current suppression device, that prevents ionic current leakage, the system being a bipolar arrangement without a bipolar plate or bipolar separator.

[0021] In some embodiments, the system comprises a control unit configured to operate two or more cells or stacks according to an operating pattern.

[0022] The systems of the invention, e.g., E-TAC systems, include a plurality of cells, e.g., a plurality of cells or at least two cells or more than two such cells, each of which is in the form of a compartment / container with at least one electrode assembly and configured to hold an aqueous / electrolyte solution. The number of cells in the systems of the invention may vary based on, among other things, the intended operation, operation pattern, etc. Each cell is configured to have a dual function such that during application of an electrical bias to the cell (bias on), hydrogen gas is produced, and in the absence of an applied bias (bias off), spontaneous generation of oxygen gas can occur.

[0023] As described in detail herein, each of the two or more cells may function as a single, independent unit configured to produce both hydrogen gas and oxygen gas by including an electrode assembly including an anode and a cathode, and it should be noted that each of the two or more cells is not a half-cell that includes an electrode and an electrolyte.

[0024] The electrode assembly comprises a cathode that produces hydrogen gas in the presence of a bias, optionally by reducing water, and further resulting in the production of hydroxide ions. The production of hydrogen gas may be under basic pH, acidic pH, or neutral pH conditions. Thus, the aqueous medium may be acidic, neutral, or basic and may be selected from tap water, seawater, carbonate / bicarbonate buffers or solutions, electrolyte-rich water, and the like. In some embodiments, the cathode is configured to affect the reduction of water molecules to produce hydrogen gas, and optionally hydroxide ions. In some other embodiments, the cathode reduces hydrogen ions in an aqueous solution to produce hydrogen gas. The cathode may be made of a material selected from metals and electrode materials used in the art. The electrode material may be selected from, for example, nickel, Raney nickel, copper, graphite, platinum, palladium, rhodium, cobalt, MoS2, and compounds thereof. In some embodiments, the electrode material is not or does not comprise cadmium (Cd). In some embodiments, the cathode is composed of Raney nickel, copper, graphite, or platinum.

[0025] The anode may comprise or consist of the same electrode materials as the cathode, but according to the present invention, the material of the anode must allow at least one redox cycle (reaction), i.e. oxidation, reduction. In other words, the anode according to the present invention can reversibly undergo an oxidation step (anode charging) in the presence of an applied bias to generate oxygen gas under the conditions described herein, followed by a subsequent reduction step (anode regeneration) in the absence of bias. Optionally, this is followed by further redox cycles. The term "reversibly" or "reversibility", when used in reference to an electrode, refers to the ability of the electrode to chemically undergo reduction / oxidation without reversing the polarity of the system. Switching the bias on / off is not considered a polarity reversal as known in the art. Thus, the reversibility of the anode can be said to be intrinsic to the electrode material.

[0026] Since the redox reaction must involve proton exchange, as further disclosed herein, the anode material must enable a redox potential greater than 1.23 V and less than 1.8 V versus a reversible hydrogen electrode (RHE). The bias voltages are measured at 25° C. as shown below.

[0027] Thus, according to some embodiments, the system comprises: at least one stack of two or more E-TAC cells, each of the cells configured to hold an electrolyte solution, each comprising at least one electrode assembly having a cathode electrode and an anode electrode, the cathode configured to affect reduction of water in the electrolyte solution in response to an applied electrical bias to produce hydrogen gas and hydroxide ions, and the anode capable of reversibly undergoing oxidation in the presence of hydroxide ions and reduction in the absence of bias to produce oxygen gas; Each of the two or more cells in the at least one stack is configured and operable to allow directional flow of electrolyte solution between adjacent cells and is connected in series to another of the two or more cells in the stack via a BPC, i.e., an ionic current interrupter or shunt current suppression device, that prevents ionic current leakage, the system being a bipolar arrangement without a bipolar plate or bipolar separator.

[0028] The present invention further provides a method for minimizing ionic shunt current in an electrochemical system, such as an E-TAC system, the system having a plurality of stacks each having a plurality of cells connected in series, the system having an electrolyte solution shared by the plurality of cells, the solution flow path being provided with a BPC, the method comprising flowing the electrolyte solution through a path provided with the BPC to at least partially reduce the shunt current compared to a system without the BPC.

[0029] Also provided is a method for minimizing ionic shunt current in an electrochemical system, the method comprising: A system having a plurality of stacks each including a plurality of electrochemical cells connected in series, the system including an electrolyte solution shared by the plurality of cells, the solution flow path between any two cells being provided with a bipolar connector (BPC); flowing an electrolyte solution through a path provided with a BPC to at least partially reduce shunt current compared to a system without the BPC; Equipped with.

[0030] The present invention further provides a method for minimizing ionic shunt currents in an electrochemical system, the system having a plurality of stacks each comprising a plurality of electrochemical cells connected in series, the system comprising an electrolyte solution shared by the plurality of cells, the solution flow path between any two cells being provided with a bipolar connector (BPC), the method comprising flowing the electrolyte solution through a path provided with the BPC to at least partially reduce ionic shunt currents in the system.

[0031] A method for minimizing ionic shunt current in an electrochemical system is provided, the method comprising: providing a system having a plurality of electrochemical cells connected in series and an electrolyte solution flowing between the plurality of cells through a conduit defining a solution flow path; Assembling a bipolar connector (BPC) along a solution flow path provided between any two cells such that the electrolyte solution flows through the BPC, thereby at least partially reducing ionic shunt current in the system; Equipped with.

[0032] As described herein, ionic current is generated and driven by the inter-cell potential gradient of the stack. When each cell in the stack shares a common electrolyte and a low resistivity path exists, shunt current occurs. "Shunt current" refers to a situation where current chooses a low resistivity path to reach the end cell. As disclosed herein, an approach developed by the inventors to achieve electrical ionic isolation while providing an electrolyte passage between the stacks includes placing a mechanical or physical bipolar connector (BPC), which is a shunt current suppression device or ionic electrical insulator, in the electrolyte solution flow path, and the structure or operation of the BPC allows uninterrupted flow of the electrolyte solution in the path and also prevents or reduces ionic shunt current (current leakage).

[0033] A bipolar connector (BPC) is not a bipolar plate or bipolar separator as known in the art. As disclosed herein and shown in Figures 4 and 5, unlike a bipolar plate or bipolar separator, a BPC according to the present invention allows for substantially uninterrupted electrolyte flow through the cell / stack while also allowing electronic conductivity. Thus, the BPC is structured to provide ionic insulation despite continuous electrolyte flow.

[0034] One or more BPCs are provided along the electrolyte flow path to separate any two electrochemical cells. BPCs may also be utilized to provide separation between stacks of electrochemical cells. In some embodiments, a BPC is provided between any two electrochemical cells in a stack at a location along the electrolyte solution flow path. In some embodiments, a BPC is provided between any two stacks at a location along the electrolyte solution flow path. In some embodiments, a BPC is provided between any two electrochemical cells and / or any two stacks in a stack at a location along the electrolyte solution flow path between the electrochemical cells or stacks.

[0035] Generally speaking, the BPC may be a continuous conduit that defines an electrolyte pathway and may be provided in a form (e.g., length, diameter or cross-section, structure, shape, inclusion of mechanical members, etc.) that suppresses or reduces ionic shunt current. Shunt current suppression or ionic electrical isolation may be achieved by various BPC configurations. In some implementations, the electrolyte pathway is reduced or disrupted by inserting gas bubbles into the electrolyte solution (exemplified in Figures 7A and 10). Additionally or alternatively, the electrolyte pathway may be lengthened and reduced in cross-section to increase the electrical resistance of the electrolyte along the pathway (Figures 7B, 8).

[0036] Shunt current suppression or ionic electrical isolation may be achieved by introducing a BPC having geometric structures or components along the electrolyte pathway.

[0037] Current leakage may be prevented by utilizing a porous plate having bore holes through the plate, the plate configured to receive electrolyte solution on the top surface of the porous plate such that the electrolyte solution flows through the bore holes (FIGS. 9A-B and 10). Gas bubbles that form during the charging step or during gas generation, e.g., hydrogen gas generation, will flow through the bore holes and block the ion path by creating an electrolyte separation / gap between two areas separated by the bipolar connector.

[0038] To minimize the pressure drop in the BPC, the mechanical resistance in the electrolyte flow paths should be reduced. To accomplish this, the device may include welds, joints, or structural modifications designed to minimize the mechanical resistance in the electrolyte flow paths.

[0039] In some embodiments, as further disclosed herein, the shunt current is reduced by increasing the electrical resistance in the electrolyte pathway, for example by testing the BPC by increasing the length of the flow path, placing the pathway in a loop pattern, introducing a transition gap, or introducing a resistive electrolyte junction.

[0040] In some embodiments, the BPC may be in the form of a moving gap (physical break) and / or a high resistance electrolyte connection introduced into the electrolyte pathway. The moving gap in the electrolyte may be realized by an isolating solid, liquid, or gas. Figures 6 and 7 show two typical implementations utilizing the moving gap approach with an isolating solid (Figure 6) or an isolating gas or liquid pocket (Figure 7A).

[0041] Figure 6 shows an approach where the BPC is in the form of a solid rotating barrier. In this approach, the rotating barrier provides separation between the "in" and "out" of the flow such that the bottom of the barrier (the first cell / stack) is always ionically and physically separated from the top of the barrier (the additional cells / stacks).

[0042] Similarly, Figure 7A shows electrolyte flow through the BPC in the form of a separate gas or liquid pocket that breaks the connection between the upper and lower electrolytes. Such gas pockets can be formed, for example, by moving a two-phase flow (gas and liquid) in a spiral channel as shown in Figure 7B. The spiral flow results in separation of the liquid and gust (due to centrifugal forces and density differences) and the formation of a gas pocket that breaks the connection between the upper and lower electrolytes.

[0043] The BPC implemented in the systems of the present invention may be an electrolyte pathway formed as a loop. The loop may be a helical loop as shown in FIG. 7B, or may be configured to take other shapes, such as, for example, an oval, a rectangle with straight or rounded ends, or any other shape. A high resistance electrolyte BPC or connection may be achieved by forming a channel within the electrolyte pathway. A simple example of such a design is shown as FIG. 8. In some embodiments, the channel is elongated, whereby the formula

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[0044] In some embodiments, the BPC is a resistive electrolyte connection. In an electrolytic device, the electrolyte contains gas bubbles that are significantly more resistive than the electrolyte. These gas bubbles increase the effective resistance of the electrolyte and improve BPC performance. A practical BPC design based on a resistive electrolyte connection is shown in FIG. 9A, which shows a side view (left) and a front view (right) of the BPC.

[0045] The BPC shown in Figure 9B is provided with several channels (channel dimensions are shown next to the figure) with conical inlets and outlets. The geometric dimensions of the channels determine the BPC pressure drop, the ionic electrical resistance, and the geometric dimensions of the metal tabs determine the electrical resistance. 1) The pressure drop (Δp) depends on the diameter of the channel (d ch ), the channel length (l ch ), the number of channels (N ch ), and the electrolyte flow rate through the BPC, 2) Ionic resistance (R ion ) is the diameter of the channel (d ch ), the channel length (l ch ), the number of channels (N ch ), and the ratio of gas flow rate to liquid electrolyte flow rate, 3) The electrical resistance (Relc) depends on the length (l), width (w), and thickness (t) of the tab.

[0046] These values ​​can be expressed in terms of the geometric dimensions of the channels, the number of channels, the parameters of the two-phase flow (electrolyte + gas hydrogen), and the electrical parameters of the electrolyte.

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[0047] In such designs, the device resistance (R ion ) and a decrease in pressure drop (Δp) are desired. However, as can be seen from equations (1) and (2), an increase in the ohmic resistance of the channel is always accompanied by an increase in the pressure drop. The second term in equation (2) is the ohmic component of the resistance

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[0048] A combined design may be utilized as a device in the E-TAC system disclosed herein. A typical design combining both moving gaps (physical disconnection) in the electrolyte pathway and high resistance electrolyte connection in the BPC is shown in FIG. 10. In the gas accumulator design shown in FIG. 10, a complex channel structure is implemented that contains voids that allow gas to accumulate in the voids and form gas pockets. These gas pockets continue to move in the channel creating electrolyte gaps.

[0049] Regardless of the BPC type, the BPC needs to be placed along the fluid electrolyte pathway. It should be understood that the BPC may be placed anywhere along the pathway to increase the length of the conduit and reduce shunt currents.

[0050] For a better understanding of the subject matter disclosed herein and to illustrate how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which: [Brief description of the drawings]

[0051] [Figure 1] 1 shows a monopolar configuration according to the state of the art. [Diagram 2] 1 shows a bipolar configuration according to the state of the art. [Diagram 3] Shows current leakage between adjacent cells. [Figure 4] 1 illustrates a bipolar operating concept according to the current state of the art. [Diagram 5] 1 illustrates a bipolar connector (BPC) operating concept according to the present invention. [Figure 6] An example of a moving gap design is provided that is in the form of a rotating solid barrier. [Figure 7A-B] Examples of a transfer gap design with an isolation pocket (FIG. 7A) and a loop design (FIG. 7B) are provided. [Figure 8] 1 provides examples of resistive electrolyte connection designs. [Figure 9A-B] Side and front views of a BPC design combining both moving gap and resistive connections are shown: Figure 9A shows the entire device and the electrical connections to the roll of devices (side and front), and Figure 9B shows the channel structure. [Figure 10] 1 illustrates a gas accumulator BPC according to some embodiments of the present invention. [Figure 11] SUMMARY OF THE DISCLOSURE A bipolar roll assembly configuration according to some embodiments of the present invention is provided. [Figure 12] Shown is the IV curve of the E-TAC reactor measured during LSV testing from 1.5 to 3.5 V. [Figure 13] Voltage measurements are shown on the E-TAC demonstration system in two configurations: monopolar (cell 1-MP) and bipolar (cell 1-BP). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0052] Two rolls, each defining an electrochemical cell (electrochemical cells 1 and 2), were assembled in an E-TAC reactor as shown in Figure 11. Between the two cells, a BPC was provided, for example as shown in Figure 10. The reactor was tested in an E-TAC demonstration system with 5M KOH electrolyte. Electrochemical measurements were performed using a 10A, 4V Ivium potentiostat channel. Example 1

[0053] In the first experiment, linear scan voltammetry (LSV) was used to characterize the onset potential for bipolar electrode operation, shown in FIG.

[0054] As shown, below 2.7V the potential was too low for the two rolls connected in series. At this voltage the low current measured was a small leakage current between the anode of the first roll and the cathode of the second roll. However, when the voltage was increased above 2.7V the current increased significantly. At this voltage there was enough voltage (>1.35V) for each roll to operate and the current measured was primarily due to the current flowing through the BPC connecting the two rolls as described above. This demonstrated that the BPC can achieve the goal of significantly reducing leakage current. Example 2

[0055] The same experimental setup was used to investigate the operation throughout the E-TAC cycle. In this experiment, the same two rolls were used in two different configurations: monopolar and bipolar. In both configurations, the current through each roll was expected to be 5A, and therefore the same hydrogen production was expected. Figure 13 shows the measured reactor voltages in the two configurations. Table 1 shows the average voltage and power consumption in each configuration. [Table 1]

[0056] Table 1 demonstrates that adding a BPC between two rolls forms a bipolar configuration, reducing the current (by a factor of 2) while doubling the voltage. This configuration reduces power consumption compared to the monopolar configuration.

Claims

1. A system comprising one or more bipolar stacks, each stack comprising two or more electrochemical cells each comprising an electrode assembly and an electrolyte solution, the cells within each stack being arranged in series and fluidly associated via an inter-cell conduit defining a flow path for the solution between the cells, the conduit comprising a bipolar connector (BPC) configured and operable to reduce or prevent current leakage while maintaining the flow of the electrolyte solution, the system being provided in a bipolar arrangement and each of the stacks being without a bipolar plate or a bipolar separator.

2. A plurality of electrochemical cells arranged in a plurality of stacks, the plurality of electrochemical cells each cell being connected in series to another cell within the stack, means for supplying an electrolyte solution as a shared electrolyte to the cells / stacks, an electrolyte conduit configured as an electrolyte flow path, the electrolyte conduit provided with a bipolar connector (BPC) configured and operable to reduce or prevent current leakage while maintaining the flow of the electrolyte solution and an electrochemical system comprising the system being provided in a bipolar arrangement and each of the stacks being without a bipolar plate or a bipolar separator.

3. The system according to claim 1, wherein the two or more electrochemical cells are stacked in a bipolar connection.

4. The system according to claim 1, provided with one or more manifolds enabling circulation of the electrolyte solution into and within the system.

5. The system according to claim 1, which is an electrochemically thermally activated chemical cell (E-TAC) electrolysis device.

6. The system according to claim 5, comprising a control unit configured to operate the two or more stacks according to an operation pattern. **Claim 7** At least one stack of two or more E-TAC cells, each of said cells being configured to hold an electrolyte solution and comprising at least one electrode assembly having a cathode electrode and an anode electrode each, said cathode being configured to produce hydrogen gas and hydroxide ions by affecting the reduction of water in said electrolyte solution in response to an applied electrical bias, said anode being capable of reversibly undergoing oxidation in the presence of hydroxide ions and reduction in the absence of said bias to produce oxygen gas, at least one stack comprising Each of the two or more cells in said at least one stack is configured and operable to allow a directional flow of said electrolyte solution between adjacent cells and is connected in series via a bipolar connector (BPC) that prevents ionic current leakage to another cell of said two or more cells in said stack, said system being in a bipolar arrangement without bipolar plates or bipolar separators, the system according to claim 5. **Claim 8** The BPC is a continuous conduit defining said electrolyte path, said conduit comprising welds or joints selected to minimize mechanical resistance in said path, the system according to claim 1. **Claim 9** The BPC is a continuous conduit defining said electrolyte path, said conduit comprising a moving gap or a resistive electrolyte connection, the system according to claim 1. **Claim 10** The moving gap is a solid, liquid, or gas for isolation, the system according to claim 9. **Claim 11** The moving gap is a gas bubble or a plurality of gas bubbles, the system according to claim 9. **Claim 12** The system according to claim 1, wherein the BPC is a solid rotating barrier.

13. The system according to claim 1, wherein the BPC is a continuous conduit defining the electrolyte path, and the conduit is arranged as a loop.

14. The system according to claim 13, wherein the loop is a spiral loop.

15. The system according to claim 1, wherein the BPC is a resistive electrolyte connection.

16. The system according to claim 1, wherein the BPC comprises a porous plate having bore holes penetrating the plate, and the plate is configured to receive the electrolyte solution on an upper surface of the porous plate so as to flow through the bore holes.

17. A method for minimizing ionic shunt current in an electrochemical system, comprising: providing a system having a plurality of stacks each comprising a plurality of cells connected in series, the system comprising an electrolyte solution shared by the plurality of cells, and a bipolar connector (BPC) being provided in a solution flow path between any two cells; flowing an electrolyte solution through the path provided with the BPC to at least partially reduce the shunt current as compared to a system without the BPC; and.

18. A method for minimizing ionic shunt current in an electrochemical system, wherein the system has a plurality of stacks each comprising a plurality of cells connected in series, the system comprises an electrolyte solution shared by the plurality of cells, and a bipolar connector (BPC) is provided in a solution flow path between any two cells, the method comprising flowing an electrolyte solution through the path provided with the BPC to at least partially reduce the ionic shunt current in the system.

19. The method according to claim 17, wherein the system is an E-TAC. **Claim 20** The method according to claim 19, wherein the system comprises a plurality of stacks, and each stack comprises two or more electrochemical cells.

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